This invention relates to devices and methods for controlling the temperature and humidity of an air supply for an environmentally controlled industrial and/or manufacturing facility that requires a continuous supply of air that meets predetermined parameters.
In various industries, the overhead costs typically associated with heating, cooling, and conditioning of an air supply can be a significant portion of the overall facilities management budget. The costs are even more pronounced in the manufacturing industries where precise temperature and humidity controls must be established and continuously maintained to meet high-quality standards and to ensure the uninterrupted, round-the-clock flow of manufactured goods. In many manufacturing processes, including for example automotive assembly line coating, and painting processes, a large amount of energy is needed to carefully control and maintain the environment. The type of compounds and chemicals required to coat and paint automotive frames, panels, and bodies mandates precise, positive control and maintenance of the ambient environment. The types of substances used for coating and painting automobile frames, components, and panels have very specific temperature and humidity requirements to promote the optimum, non-anomalous application, drying, and curing times required by the coatings.
Ordinarily, the environmental control systems in use for certain parts of large manufacturing operations must be capable of supplying an environment with a continuous flow of clean air at a specific temperature and humidity. The air supply source is typically fresh, outside air, or recycled air. Such control systems often sacrifice energy efficiency in favor of a large capacity for heating, cooling, and conditioning, so that a treated air supply can be guaranteed despite the condition of the air supply source air flow. This capability for an uninterrupted supply of conditioned air is especially important in manufacturing operations that are run continuously and that use an unpredictable source of outside, ambient or recycled air as the incident air stream source. The use of either recycled or outside air can require that a large amount of energy be added or removed from the supply air to achieve the desired, precise air temperature and condition. Furthermore, considerable amounts of energy can be required to humidify or dehumidify outside to air to meet the desired humidity level.
Some attempts have been made to improve the energy efficiency of air supply control systems. Attempts to improve the energy efficiency of large-scale air supply systems have incorporated components such as specialized circulation and valve systems as well as variable frequency drives to vary fan speeds to decrease the energy consumption requirements of the air supply control system during times of reduced demand for conditioned air.
For example, efforts have been made to control the rate of air flow through a medical isolation control environment using many different types of subsystems, including heating, cooling, air flow rate, humidification, and filtering subsystems. However, these types of air supply control system are unnecessarily expensive and complicated to install, and inefficient for use in the large scale air supply systems needed for most automotive manufacturing processes. U.S. Pat. No. 5,538,471 is limited to a medical isolation environmental control system that includes many such subsystems and which also includes a variable frequency drive operative to control the air flow rate.
Other prior art devices have been directed to air control systems for use in the semiconductor manufacturing industries that are also unsuitable for use in automotive manufacturing operations. U.S. Pat. No. 5,851,293 is directed to a system that treats the effluent gases resulting from semi-conductor manufacturing processes, which uses a variable frequency drive to modulate the flow of the hot effluent gas stream. The described effluent gas treatment capability is not be readily adapted for use in the automotive manufacturing processes, which require a higher volume, more energy efficient air supply system. Attempts to improve diary cow milking systems have included vacuum control systems that incorporate a variable frequency drive to control the vacuum level of an air reservoir included in the milking system. U.S. Pat. Nos. 5,878,691 and 5,845,599 are directed to these types of milking systems. However, these prior art milking control systems cannot be adapted for use in the automotive manufacturing processes taught by the instant invention.
None of the preceding references disclose or suggest the use of a variable frequency drive in the cooling unit of an air supply control system to control the rate of cooling of an air supply control system that includes a cooling unit, a heating unit, and a programmable logic controller configured to monitor the air supply temperature and to adjust it by activating the cooling and heating units.
What has been needed, but heretofore unavailable, is an improved, more energy efficient, environmental air supply control system that is compatible for use with the large scale air supply requirements commonly found in automotive manufacturing operations. As is well known, the automotive manufacturing industry is highly competitive in terms of minimizing operational costs. Every cost savings can often be directly passed through to the consumer in reduced automobile prices. Any reduction in the amount of energy consumed during the various manufacturing processes can result in large cost savings in light of the large economies of scale. This is especially true in automotive manufacturing processes that are in continuous operation throughout multiple daily shifts. Any manufacturing process that is inefficient or unnecessarily expensive because of an unnecessary waste of energy can result in the manufacturer suffering economically from the costs of the wasted energy resources. This economic loss may translate directly to higher prices and sales lost to competitors that have improved their manufacturing processes, saved on energy costs, and reduced the consumer price of competitive products.
The air supply control system of the present invention offers a solution to the problem of excessive energy consumption in the air supply control and conditioning systems. The inventive solution accomplishes this by reducing the number mechanical parts as compared with previous systems, and by improving the operational efficiency of, and by incorporating variable frequency drives to control critical cooling fluid flow through the air supply control system to optimize conditioning capability and minimize energy consumption.
In general, the present invention relates to an improved air supply control device for maintaining and supplying an airflow at a predetermined temperature. The device includes a cooling unit that is adapted to cool the air passing through the unit, which includes a variable speed cooling fluid pump that pumps cooling fluid through a heat exchanger in the cooling unit, and a variable frequency drive (xe2x80x9cVFDxe2x80x9d) that is electrically connected to the pump and which can vary the speed of the pump. The device also incorporates a temperature sensor that is positioned to detect the temperature of the air after it has passed through the cooling unit. A programmable logic controller (xe2x80x9cPLCxe2x80x9d) is included in the device and is in electronic communication with the temperature sensor and the VFD. The PLC is programmed to monitor the temperature of the air and to vary the speed of the cooling fluid pump to adjust the temperature of the air passing through the cooling unit to the predetermined temperature.
The present invention is also directed to an air temperature and humidity control device that is configured to maintain and supply an airflow at a predetermined temperature and humidity. The device includes a cooling unit that is operative to cool the air passing through the unit, and includes a variable speed cooling fluid pump that pumps cooling fluid through a heat exchanger in the cooling unit. A VFD is electrically connected to the cooling fluid pump and is adapted to vary the speed of the pump for changing the amount of fluid pumped through the heat exchanger. The control device further includes a temperature controller with a temperature sensor that is positioned inside the control device to detect the temperature of the air after it passes through the cooling unit. A PLC is also incorporated and it is in electronic communication with the temperature controller or sensor, or both, and the VFD, and is programmed to vary the speed of the cooling fluid pump to adjust the temperature of the air passing through the cooling unit to the predetermined temperature. The temperature and humidity control device also includes a humidity control unit positioned in the air flow that includes an air humidifier and a humidity sensor operative to adjust the humidity of the air flow if it deviates from the predetermined humidity. A heating unit may also be electronically coupled to the PLC and is operative to heat the airflow in response to signals from the PLC. Also, the PLC is programmed to delay adjustments to the VFD to change the speed of the cooling pump motor for an interval of time that allows the cooling unit to reach a stable heat exchange rate before additional changes are made by adjusting the speed of the pump motor. This feature accounts for the latency period required for the cooling unit, and the air flowing through it, to respond to previous changes.
The preceding embodiments of the present invention also contemplate a variation that includes a thermostat having a temperature selector configured to be set to the predetermined temperature. The PLC in this variation is in electronic communication with the thermostat, the temperature sensor, and the VFD, and it is programmed to vary the speed of the cooling fluid pump to adjust the temperature of the air passing through the cooling unit when the predetermined temperature is different from the temperature indicated by the temperature sensor.
In another variation of the preceding embodiments, the PLC is in electronic communication with the temperature sensor and the VFD, and it includes a temperature selector that is adapted to be programmed to the predetermined temperature. The PLC is programmed to vary the speed of the cooling fluid pump to adjust the temperature of the air passing through the cooling unit to the predetermined temperature set by the selector. Each of the preceding embodiments and variations also contemplate a PLC that is in electronic communication with a computer that is configured to monitor and reprogram the PLC.
The present invention is also directed to a VFD controlled air cooling unit for maintaining the temperature of an air flow supply at a predetermined temperature that includes a variable speed cooling fluid booster pump in fluid communication with a pressurized cooling fluid supply and a VFD in electronic communication with the pump and configured to vary the cooling fluid flow rate through the pump. This variation of the preceding embodiments of the invention also includes a temperature sensor positioned to detect the temperature of the air after it has passed through the cooling unit and a PLC adapted to communicate electronically with the temperature sensor and the VFD. The PLC is programmed to adjust the VFD to increase and decrease the speed of the cooling fluid pump to boost the cooling fluid pressure to maintain the temperature of the air passing through the cooling unit at the predetermined temperature.
In another variation of the preferred embodiments of the instant invention, there is disclosed an air supply control device for maintaining and supplying an airflow at a predetermined temperature. This variation incorporates a cooling fluid source that supplies pressurized cooled liquid and a cooling unit adapted to cool the air passing through the unit that includes a variable speed, cooling fluid boost pump in fluid communication with a check valve that is connected to the cooling fluid source. A VFD is also included that is electrically connected to the pump and adapted to vary its speed. The device further includes a temperature sensor positioned to detect the temperature of the air after it has passed through the cooling unit, and a PLC in electronic communication with the check valve, the temperature sensor, and the VFD and programmed to actuate the check valve and to vary the speed of the cooling fluid pump to adjust the temperature of the air passing through the cooling unit to the predetermined temperature.
The instant invention is also directed to a method for maintaining and supplying at a predetermined temperature an air flow moving through a cooling unit that incorporates a variable speed, cooling fluid pump motor controlled by a VFD responsive to a PLC programmed to sense the temperature indicated by a sensor positioned proximate to the flowing air and to adjust the pump motor speed to vary the cooling rate of the cooling unit. The method includes the steps of monitoring the temperature of the air flow leaving the cooling unit with the PLC detecting the temperature indicated by the sensor, and increasing the temperature of the air flow if it falls below the predetermined temperature wherein the PLC sends a signal to the VFD to decrease the speed of the variable speed cooling fluid pump to reduce the cooling rate of the cooling unit. The method also includes the step of decreasing the temperature of the air flow if it exceeds the predetermined temperature wherein the PLC sends a signal to the VFD to increase the speed of the variable speed cooling fluid pump to increase the cooling rate of the cooling unit.